CN115298947A - DC-DC Converter with Freewheeling Circuit - Google Patents

Abstract

The present invention relates to a DC-DC DC-DC converter for two-port and three-port topologies and the like. The DC-DC converter includes: a first port coupled to a first full bridge; and a transformer coupled to the first and second full bridges. The DC-DC converter further includes: a second port coupled to the second full bridge; a first inductor coupled between the second full bridge and the second port; a first freewheeling circuit, A first diode coupled in series with the switch is included. The first freewheel circuit is also coupled in parallel with the first inductor between the second full bridge and the second port. Therefore, the DC-DC converter has a wide input wide output WIWO range and linear voltage gain.

Description

DC-DC Converter with Freewheeling Circuit

technical field

The invention relates to a direct current (DC)-to-direct converter with a freewheeling circuit, that is, a DC-DC converter.

Background technique

Electric vehicles have demanding requirements for power density, cost and system integration. On the other hand, automotive original equipment manufacturers (OEMs) require bi-directional power transmission. Therefore, an on board charger (OBC) with a three-port DC-DC output stage after power factor correction (power factor correction, PFC) is a trend in OBC design in the future. Different three-port topologies are known for DC-DC converters.

One such traditional three-port topology is a dual active bridge (DAB) based bidirectional DC-DC converter. DAB technology has high reactive power at light and medium loads when using single phase shift (SPS) modulation. In order to achieve higher efficiency at light or medium load conditions, TPS modulation is required, which is a complex control algorithm that is often difficult to implement. Applying TPS control in a three-port topology is more challenging.

One such traditional three-port topology is the resonant scheme topology that is often used to improve system efficiency. Although this scheme can achieve higher efficiency, it is difficult for the LLC topology to meet the requirements of wide input and wide output (WIWO). When the input/output voltage range of a DC-DC converter exceeds 40% of its nominal input/output voltage, it is considered WIWO.

Contents of the invention

An object of embodiments of the present invention is to provide a solution to reduce or solve the disadvantages and problems of conventional solutions.

Another object of the examples of the present invention is to provide a novel topology which is particularly suitable for bidirectional DC-DC conversion with wide input wide output voltage requirements in any application requiring high efficiency and high power density bidirectional power transmission device.

The above and other objects are achieved by the subject matter claimed by the independent claims. Further advantageous examples of the invention can be found in the dependent claims.

According to a first aspect of the present invention, the above and other objects are achieved by a DC-DC converter comprising:

The first port includes: a first side for coupling to a DC bus; a second side for coupling to a first full bridge, wherein the first full bridge includes a first switch, a second switch, a third switch, and a first full bridge. Four switches;

A transformer comprising: a primary winding coupled to the first full bridge; a secondary winding coupled to the second full bridge, wherein the second full bridge includes a fifth switch, a sixth switch, a seventh switch and an eighth switch;

a second port comprising: a first side coupled to the second full bridge; a second side coupled to the first battery;

a first inductor coupled between the second full bridge and the first side of the second port;

A first freewheeling circuit, comprising a first diode coupled in series with the ninth switch, wherein the first freewheeling circuit is coupled in parallel with the first inductor between the second full bridge and the second port between the first sides of the .

Ports in this context may be considered input and/or output terminals. Thus, the ports can be used to act as inputs or outputs depending on the operating mode of the DC-DC converter.

The full bridge in this paper can be understood as two half bridges coupled or connected in parallel with each other. A half bridge can be constructed with two switches and two freewheeling diodes.

The DC-DC converter may operate in a forward mode with a current direction from the first port to the second port. The DC-DC converter may also operate in a reverse mode with the direction of current flow from the second port to the first port.

An advantage of the DC-DC converter according to the first aspect is that it has a wide input wide output range suitable for electric vehicle applications and the like. Furthermore, the voltage gain of the DC-DC converter is linear.

According to the first aspect, in an implementation manner of the DC-DC converter, the DC-DC converter is used in the first reverse mode from the second port to the first port in the current direction When working under:

i) operating said ninth switch in a saturation region of said ninth switch;

ii) turning on the fifth switch and the eighth switch within a first time period,

iii) turning off the fifth switch, the sixth switch, the seventh switch and the eighth switch during a second time period after the first time period,

iv) turning on the sixth switch and the seventh switch during a third time period subsequent to the second time period,

v) turning off the fifth switch, the sixth switch, the seventh switch and the eighth switch during a fourth time period after the third time period;

Repeat ii) to v) until the voltage at the DC bus is equal to or higher than the first threshold voltage.

In the present invention, the conduction of a switch can be understood as that the switch has low impedance and can conduct current.

In the present invention, a switch OFF may be understood as the switch has a high impedance and cannot conduct current.

An advantage of the DC-DC converter according to this implementation is that a soft start function of said first reverse mode operation is provided.

According to the first aspect, in an implementation manner of the DC-DC converter, the DC-DC converter further includes:

A first protection circuit coupled between the second full bridge and the first side of the second port and connected in parallel with the second full bridge.

The advantage of the DC-DC converter according to this implementation is that the switch at the second port can be protected from failure of the controller used to control the switch of the DC-DC converter The impact of overvoltage/overcurrent caused by etc.

According to the first aspect, in an implementation manner of the DC-DC converter, the first protection circuit includes:

a first zener diode and a second zener diode, the first zener diode and the second zener diode being coupled in series with each other and in opposite directions; or

first varistor.

According to the first aspect, in an implementation manner of the DC-DC converter, the DC-DC converter further includes:

A third port comprising: a first side coupled to a Y circuit; a second side coupled to a second battery, wherein the Y circuit is coupled to a center tap winding of the transformer and includes an eleventh switch, A twelfth switch and a thirteenth switch.

An advantage of the DC-DC converter according to this implementation is that the DC-DC converter is able to transfer energy/power to the third port. Furthermore, there is no energy decoupling between the second port and the third port.

According to the first aspect, in one implementation of the DC-DC converter, the source pin or the emitter pin of each switch is coupled to a common node of the Y circuit.

An advantage of the DC-DC converter according to this implementation is that the voltage at the third port can be modulated when the third port is configured as an output port.

According to the first aspect, in an implementation manner of the DC-DC converter, the first battery is a high-voltage battery, and the second battery is a low-voltage battery.

An advantage of the DC-DC converter according to this implementation is that it can transfer energy/power between the high voltage battery and the low voltage battery and vice versa.

According to the first aspect, in an implementation manner of the DC-DC converter, the DC-DC converter further includes:

a second inductor coupled between the Y circuit and the first side of the third port;

The second freewheeling circuit includes a second diode coupled in series with the tenth switch, wherein the second freewheeling circuit is coupled in parallel with the second inductance to all of the Y circuit and the third port between the first side described above.

An advantage of the DC-DC converter according to this implementation is that the third port can be used for sending or receiving power/energy.

According to the first aspect, in an implementation manner of the DC-DC converter, the DC-DC converter is used in the second reverse mode from the third port to the first port in the current direction When working under:

i) controlling the tenth switch to work in its saturation region,

ii) turning on the twelfth switch;

iii) turning on the eleventh switch within a first time period,

iv) turning off said eleventh switch and said thirteenth switch during a second time period after said first time period,

v) turning on the thirteenth switch during a third time period subsequent to the second time period,

vi) turning off the eleventh switch and the thirteenth switch within a fourth time period after the third time period;

Repeat iii) to vi) until the voltage at the DC bus is equal to or higher than the second threshold voltage.

An advantage of the DC-DC converter according to this implementation is that this implementation provides a soft start function for said second reverse mode operation.

According to the first aspect, in an implementation manner of the DC-DC converter, the DC-DC converter further includes:

a second protection circuit coupled between the Y circuit and the first side of the third port.

The advantage of the DC-DC converter according to this implementation is that the switch at the third port can be protected from failure of the controller used to control the switch of the DC-DC converter The impact of overvoltage/overcurrent caused by etc.

According to the first aspect, in an implementation manner of the DC-DC converter, the second protection circuit includes:

a third zener diode and a fourth zener diode, the third zener diode and the fourth zener diode being coupled in series with each other and in opposite directions; or

second varistor.

According to the first aspect, in an implementation manner of the DC-DC converter, the DC-DC converter further includes:

A freewheeling diode is coupled in parallel with the second protection circuit and forms a freewheeling path when the third port works as an output port.

An advantage of the DC-DC converter according to this implementation is that the output voltage at the third port can be controlled.

According to the first aspect, in an implementation manner of the DC-DC converter, the DC-DC converter further includes at least one of the following components:

a first current sensor coupled between the second full bridge and the first side of the second port and configured to provide a first set of measured current values;

a second current sensor coupled between the Y circuit and the first side of the third port and configured to provide a second set of measured current values;

A controller for controlling the switch of the DC-DC converter according to at least one of the first set of measured current values and the second set of measured current values.

The advantage of the DC-DC converter according to this implementation is that the switches of the DC-DC converter can be controlled according to the first set of measured current values and the second set of measured current values to improve switch.

According to the first aspect, in an implementation manner of the DC-DC converter, the DC-DC converter further includes:

A clamping circuit includes a first clamping diode, a second clamping diode and a clamping inductance, wherein the clamping inductance is coupled between the first full bridge and the primary winding of the transformer.

Other applications and advantages of examples of the invention will become apparent from the following detailed description.

Description of drawings

The accompanying drawings are intended to illustrate and illustrate different examples of the invention, in which:

- Figure 1 shows a DC-DC converter with a two-port topology provided by an example of the present invention;

- Figure 2 shows a DC-DC converter with a two-port topology provided by an example of the invention;

- Figure 3 shows a DC-DC converter with a three-port topology provided by an example of the present invention;

- Figure 4 shows an example of how a DC-DC converter is coupled to an external device;

- Figure 5 shows a timing diagram provided by an example of the present invention;

- Figure 6 shows a timing diagram provided by an example of the present invention;

- Figure 7 shows a timing diagram provided by an example of the present invention;

- Figure 8 shows a system overview diagram of a DC-DC converter provided by an example of the present invention;

- Figure 9 shows a DC-DC converter with a three-port topology provided by another example of the present invention;

- Figure 10 shows a DC-DC converter with a three-port topology provided by another example of the present invention;

- Figure 11 shows a DC-DC converter with a three-port topology provided by another example of the present invention.

Detailed ways

The so-called phase shift full bridge (PSFB) topology for DC-DC converters is widely used in industry due to its WIWO capability and the ability to control such PSFB converters using simple control algorithms. The reverse operation of the PSFB is a boost converter with galvanic isolation provided by the transformer. However, there are two problems with this PSFB converter.

The first problem is that when operating in reverse mode, a boost converter typically requires a soft-start phase before steady-state operation. For boost converters without isolation between input and output, a soft-start function can be easily implemented with relays and power resistors. However, this solution is not suitable for isolated boost converters due to the presence of isolation, i.e. transformer.

The second problem is that when the PSFB converter operates in reverse mode, it acts as a current source converter, e.g. induced by errors of the microcontroller or other control mechanisms of the converter. The stored energy can cause an overvoltage across the converter's switches, which can damage the converter's switching elements.

Accordingly, two-port and three-port DC-DC converter topologies are disclosed herein that can address the above issues. The two-port DC-DC converter and the three-port DC-DC converter provided by the present invention are respectively suitable for the two-port bidirectional DC-DC conversion and the three-port bidirectional DC-DC conversion of the WIWO voltage of the power regulation system. The disclosed DC-DC converter can be used in many applications such as electric vehicle (EV), on board charger (OBC), or any other application requiring two-port or three-port bidirectional DC-DC power conversion .

FIG. 1 shows a DC-DC converter 100 with a two-port topology provided by an example of the present invention. The DC-DC converter 100 includes: a first port P1 for coupling to the DC bus 202 ; a second port P2 for coupling to the first battery 204 . Accordingly, the DC-DC converter 100 is configured to be coupled between the DC bus 202 and the first battery 204 and can perform bidirectional power conversion between the DC bus 202 and the first battery 204 . The DC-DC converter 100 can operate as a buck/boost converter.

Referring to FIG. 1 , the first port P1 includes: a first side S1 _P1 for coupling to the DC bus 202 ; a second side S2 _P1 for coupling to the first full bridge 150 . The first full bridge 150 includes a first switch M1 , a second switch M2 , a third switch M3 and a fourth switch M4 .

The DC-DC converter 100 further includes a transformer Tr, and the transformer Tr includes: a primary winding PW coupled to the first full bridge 150 ; a secondary winding coupled to the second full bridge 160 . The second full bridge 160 includes a fifth switch M5, a sixth switch M6, a seventh switch M7 and an eighth switch M8.

The second port P2 includes: a first side S1 _P2 coupled to the second full bridge 160 ; a second side S2 _P2 coupled to the first battery 204 . In FIG. 1 , the upper side of the second port P2 is the first coupling point C1P2 of the second port P2, and the lower side is the second coupling point C2P2 of the second port P2.

The first full bridge 150 has four connection/coupling points/nodes, namely 152, 154, 156 and 158, and can be coupled between the second side S2 _P1 of the first port P1 and the primary winding PW of the transformer Tr in the following manner :

• The first connection point 152 of the first full bridge 150 is coupled to the first coupling point C1P1 of the first port P1 , while the second connection point 154 of the first full bridge 150 is coupled to the second coupling point C2P1 of the first port P1 .

The third connection point 156 of the first full bridge 150 is connected to the first connection point 180 of the primary winding PW of the transformer Tr, while the fourth connection point 158 of the first full bridge 150 is coupled to the second connection point of the primary winding PW of the transformer Tr. Junction point 182.

· In the first full bridge 150, the first switch M1 is coupled between the first connection point 152 and the third connection point 156, the second switch M2 is coupled between the second connection point 154 and the third connection point 156, the second Three switches M3 are coupled between the first connection point 152 and the fourth connection point 158 , and the fourth switch M4 is coupled between the second connection point 154 and the fourth connection point 158 .

The second full bridge 160 also has four connection/coupling points, namely 162, 164, 166 and 168, and is coupled between the secondary winding SW of the transformer Tr and the first side S1 _P2 of the second port P2 by:

The first connection point 162 of the second full bridge 160 is coupled/connected to the first connection point 184 of the secondary winding SW of the transformer Tr, while the second connection point 164 of the second full bridge 160 is coupled to the secondary winding of the transformer Tr The second connection point 186 of SW.

The third connection point 166 of the second full bridge 160 is coupled to the high voltage side of the first side S1 _P2 of the second port P2, while the fourth connection point 168 of the second full bridge 160 is coupled to the first side of the second port P2 Low voltage side of S1 _P2 .

In the second full bridge 160, the fifth switch M5 is coupled between the first connection point 162 and the third connection point 166, the sixth switch M6 is coupled between the first connection point 162 and the fourth connection point 168, the second The seventh switch M7 is coupled between the second connection point 164 and the third connection point 166 , and the eighth switch M8 is coupled between the second connection point 164 and the fourth connection point 168 .

The DC-DC converter 100 further includes: a first inductor L1 coupled between the second full bridge 160 and the first side S1 _P2 of the second port P2. The first inductance L1 acts as a controllable output filter for the second port P2. In FIG. 1 , the first inductor L1 is coupled between the third connection point 166 of the second full bridge 160 and the upper side of the first side S1 _P2 of the second port P2 . Thus, in this example, the first inductance L1 is coupled to the upper side of the second port P2, which is the high voltage (HV) side in FIG. 1 . However, in various examples, the first inductance L1 may instead be coupled to the underside of the second port P2, as described later in connection with FIGS. 8-10 .

The DC-DC converter 100 further includes: a first freewheeling circuit 110 forming an alternative current path to the current path passing through the first inductor L1. The function of the first freewheeling circuit 110 is to perform a loop operation during ramp-up (ie, before reaching a steady state). The first freewheeling circuit 110 includes a first diode D1 coupled in series with the ninth switch M9. The first freewheeling circuit 110 is coupled in parallel with the first inductor L1 between the second full bridge 160 and the first side S1 _P2 of the second port P2. In the example shown in FIG. 1, this means that the first freewheeling circuit 110 is coupled between the first connection point 112 and the second connection point 114 of the first freewheeling circuit 110, while the first connection point 112 is coupled to the second connection point 114 of the first freewheeling circuit 110. The third connection point 166 of the second full bridge 160, the second connection point 114 is coupled to the upper side of the first side S1 _P2 of the second port P2.

In the example of the present invention, the DC-DC converter 100 further includes: a first protection circuit 120 for protecting the switches (M5, M6, M7, M8) of the second full bridge 160 from The impact of overvoltage or overcurrent caused by energy in the battery, etc., and release when a power failure occurs. The first protection circuit 120 may be coupled between the second full bridge 160 and the first side S1 _P2 of the second port P2 and connected in parallel with the second full bridge 160 . 1, the first protection circuit 120 may have a first connection point 122 and a second connection point 124, wherein the first connection point 122 is coupled to the third connection point 166 of the second full bridge 160, and the second connection point 124 is coupled to To the fourth connection point 168 of the second full bridge 160 .

In an example of the present invention, the first protection circuit 120 may include a first zener diode Z1 and a second zener diode Z2, the first zener diode Z1 and the second zener diode Z2 are connected in series with each other and coupled in opposite directions, as Figure 1 shows. Alternatively, the first protection circuit 120 may include a first piezoresistor, but the first piezoresistor is not shown in the figure. The rated voltage of the first zener diode, the second zener diode and the first varistor should be lower than the rated voltage of the switches (M5, M6, M7, M8).

FIG. 2 shows a DC-DC converter 100 with a two-port topology provided by an example of the present invention, wherein the DC-DC converter 100 includes a clamping circuit 140 . In addition to the components described in connection with the DC-DC converter 100 shown in FIG. 1 , the DC-DC converter 100 shown in FIG. 2 also includes a clamping circuit 140 . The clamping circuit 140 includes a first clamping diode D _Clamp1 , a second clamping diode D _Clamp2 and a clamping inductor L _Clamp , wherein the first clamping diode D _Clamp1 , the second clamping diode D _Clamp2 and the clamping inductor L _Clamp is coupled between the first full bridge 150 and the primary winding PW of the transformer Tr.

2, the first clamping diode D _Clamp1 can be coupled between the first connection point 152 of the first full bridge 150 and the upper side of the primary winding PW of the transformer Tr, and the second clamping diode D _Clamp2 can be coupled between the first connection point 152 of the transformer Tr. Between the second connection point 154 of the full bridge 150 and the lower side of the primary winding PW of the transformer Tr, the clamping inductance L _Clamp may be coupled between the fourth connection point 158 of the first full bridge 150 and the lower side of the primary winding PW of the transformer Tr. between the sides.

The function of the clamp circuit 140 is to reduce the overshoot voltage on the switches M5 and M8.

FIG. 3 shows a DC-DC converter 100 with a three-port topology provided by an example of the present invention. Therefore, the DC-DC converter 100 also comprises a third port P3 comprising: a first side S1 _P3 coupled to the Y circuit 170 through its first connection point C1P3 and its second connection point C2P3; a second side S2 _P3 , for coupling to the second battery 206 (as shown in FIG. 4 ). The Y circuit 170 is coupled to the center-tapped winding CTW of the transformer Tr, and includes an eleventh switch M11 , a twelfth switch M12 and a thirteenth switch M13 .

In an example of the invention, the source or emitter pin of each switch is coupled to a common node N of the Y circuit 170 and the common node N is coupled to the first connection point 190 of the center tapped winding CTW. Furthermore, a first connection point 172 of the Y-circuit 170 is coupled to a second connection point 192 of the center-tapped winding CTW, a second connection point 174 of the Y-circuit 170 is coupled to a third connection point 194 of the center-tapped winding CTW of the transformer Tr, and The third connection point 176 of the Y circuit 170 is coupled to the second connection point C2P3 of the third port P3, as shown in FIG. 3 .

The common function of the Y circuit 170, the third diode D3 and the second inductor L2 is to form a local step-down converter, and when the third port P3 is configured as an output port, it can control the output voltage of the third port P3.

The DC-DC converter 100 further includes: a second inductance L2 coupled between the Y circuit 170 and the first connection point C1P3 of the third port P3; a second freewheeling circuit 110' comprising a series-coupled tenth switch M10 the second diode D2. The second freewheeling circuit 110' is coupled in parallel with the second inductance L2 between the Y circuit 170 and the first side S1 _P3 of the third port P3.

In the example shown in FIG. 3, this means that the second freewheeling circuit 110' is coupled between the first connection point 112' and the second connection point 114' of the second freewheeling circuit 110', while the first connection point 112' is coupled to the center of the center tapped winding CTW of the transformer Tr and the second connection point 114' is coupled to the upper side of the first side S1 _P3 of the third port P3. The second inductor L2 and the second freewheeling circuit 110' can also be located in other positions, as will be further described below in conjunction with FIGS. 8 to 10 .

In a similar manner to the first freewheeling circuit 110, the second freewheeling circuit 110' forms an alternative current path. In this case, an alternative current path to the current path through the second inductance L2.

In an example of the present invention, the three-port topology shown in FIG. 3 further includes: a second protection circuit 120' coupled between the Y circuit 170 and the first side S1 _P3 of the third port P3. When the third port P3 works as an input port, the second protection circuit 120' can act as a freewheeling circuit. Therefore, the Y circuit 170 is protected from overvoltage, overcurrent, etc. due to the energy stored in the second inductor L2, and released when a power failure occurs. The rated voltage of the components in the second protection circuit 120' should be lower than the rated voltage of the switches M11 and M12.

Referring to FIG. 3, the second protection circuit 120' may have a first connection point 122' and a second connection point 124', wherein the first connection point 122' is coupled to the center of the center tapped winding CTW of the transformer Tr, and the second connection point 124 ′ is coupled to a third connection point 176 of Y circuit 170 . The second protection circuit 120' may include a third zener diode Z3 and a fourth zener diode Z4, the third zener diode Z3 and the fourth zener diode Z4 are connected in series with each other and coupled in opposite directions, as shown in FIG. 3 . Alternatively, the second protection circuit 120' may include a second piezoresistor (not shown in the figure).

The DC-DC converter 100 with the three-port topology may further include: a freewheeling diode D3 coupled in parallel with the second protection circuit 120' and forming a freewheeling path when the third port P3 works as an output port. Therefore, when the current flows from the first port P1 to the third port P3 or from the second port P2 to the third port P3, the freewheeling diode D3 can act as a freewheeling diode, because when the switch M12 is turned off, the second inductance L2 Current will flow through freewheeling diode D3 instead of switch M12. The freewheeling diode D3 is coupled in parallel with the second protection circuit 120', and thus may be coupled between the first connection point 122' and the second connection point 124' of the second protection circuit 120', as shown in FIG.

It should be noted that the three-port topology shown in FIG. 3 also includes an optional clamping circuit 140 such as, but not limited to, the clamping circuit 140 disclosed in FIG. 2 and explained above. Furthermore, any of the above-described examples of DC-DC converter 100 may include one or more clamping circuits 140, and one or more first protection circuits 120 and/or second protection circuits 120'.

Fig. 4 shows a non-limiting example of how the DC-DC converter 100 can be coupled to different external devices. In general, the DC-DC converter 100 includes: a first port P1 for coupling to the DC bus 202 ; a second port P2 for coupling to the first battery 204 . For example, the first battery 204 may be a high voltage battery. The DC-DC converter 100 may operate in a forward mode in which current flows from the first port P1 to the second port P2. The DC-DC converter 100 can also operate in a reverse mode where current flows in the opposite direction, ie from the second port P2 to the first port P1 .

In an example, the DC-DC converter 100 further includes the third port P3 as described above. The third port P3 is used for coupling to the second battery 206 . Therefore, the DC-DC converter 100 can also operate in the second reverse mode in which the current flows in the direction from the third port P3 to the first port P1. However, current can also flow from the second port P2 to the third port P3 or from the third port P3 to the second port P2.

When the DC-DC converter 100 includes a third port P3 coupled to the second battery 206, the first battery 204 may be a high voltage battery and the second battery 206 may be a low voltage battery. For example, high voltage may refer to a voltage higher than 100V, and low voltage may refer to a voltage lower than 100V herein. Additionally, other values may be used to define high and low pressures, and such values are within the scope of the present invention.

Further details relating to the operation of the two-port and three-port DC-DC converter 100 in forward mode and reverse mode will now be described in conjunction with FIGS. 5 and 6 .

The DC-DC converter 100 with a two-port topology can operate in a first reverse mode BM1, in which energy is transferred from the second port P2 to the first port P1, ie the current direction is from the second port P2 to the first port P1. A port P1. When the DC-DC converter 100 operates in the first reverse mode BM1 with the current direction from the second port P2 to the first port P1, the DC-DC converter 100 can be used for:

i) operating the ninth switch M9 in the saturation region of the ninth switch M9;

ii) turning on the fifth switch M5 and the eighth switch M8 within the first time period,

iii) turning off the fifth switch M5, the sixth switch M6, the seventh switch within the second time period after the first time period

M7 and the eighth switch M8,

iv) turning on the sixth switch M6 and the seventh switch M7 within a third time period after the second time period,

v) turning off the fifth switch M5, the sixth switch M6, the seventh switch M7 and the eighth switch M8 within a fourth time period after the third time period;

Repeat ii) to v) until the voltage at the DC bus 202 is equal to or higher than the first threshold voltage.

The switch or switching element in the present invention may be silicon metal oxide semiconductor field effect transistor (metaloxid semiconductor field effect transistor, MOSFET), silicon carbide MOSFET, insulated gate bipolar transistor (insulated gate bipolar transistor, IGBT) and gallium nitride power Transistors, etc. Therefore, it is well known to those skilled in the art that a switch operates in its saturation region.

In the first reverse mode BM1, the DC-DC converter 100 operates in a soft start procedure. Through the soft-start procedure of the DC-DC converter 100, the voltage at the first port P1 can be charged to the same or approximately the same voltage as the first threshold voltage at the second port P2 before steady-state operation, that is, the first port The capacitance of P1 is charged from zero voltage to the same or substantially the same voltage as the first threshold voltage at the second port P2. Therefore, the surge current flowing into the first port P1, which may damage or destroy the first port P1, can be avoided. The value of the first threshold voltage can be obtained by the following equation:

The first threshold voltage = V ₂ /N ₂ *N ₁

Where, V2 is the battery voltage at the _second port P2, N1 is the winding number _of the primary winding, and _N2 is the winding number of the secondary winding.

During the soft-start procedure, the ninth switch M9 is in a semi-conductive state in step i), ie operates in its saturation region. Therefore, a freewheeling path is provided for the current of the first inductor L1, and the first inductor L1 is demagnetized. The switches ( M1 , M2 , M3 , M4 ) of the first full bridge 150 are turned off during soft-start and conduct current only through their respective body diodes.

FIG. 5 shows a timing diagram of the DC-DC converter 100 operating in the first reverse mode BM1 , wherein the DC-DC converter 100 has the two-port topology including the clamping circuit 140 shown in FIG. 2 . In FIG. 5, the gate control signals of the switches (M5, M6, M7, M8) of the second full bridge 160 and the ninth switch M9, as well as the first inductor L1, the first diode D1 and the transformer Tr The current of the secondary winding SW (indicated as transformer P2 side winding in Figure 5).

As shown in FIG. 5 , during the first time interval between the first time instance T1 and the second time instance T2 , both the fifth switch M5 and the eighth switch M8 are turned on, and this step corresponds to the above step ii). The current flows through the first inductor L1, the fifth switch M5, the eighth switch M8 and the secondary winding SW of the transformer Tr, and the energy passes through the body diode of the first switch M1, the second clamping diode D _Clamp2 and the primary winding PW of the transformer Tr transmitted to the first port P1.

During the second time interval between the second time instance T2 and the third time instance T3, the fifth switch M5 to the eighth switch M8 are all turned off, corresponding to step iii). The current flows through the freewheeling current path of the first freewheeling circuit 110 , that is, through the first diode D1 and the ninth switch M9 . This step (ie step iii)) aims at demagnetizing the first inductor L1, ie reducing the current of the first inductor L1.

During the third time interval between the third time instance T3 and the fourth time instance T4, the sixth switch M6 to the seventh switch M7 are all turned on, corresponding to step iv). The current flows through the first inductor L1, the secondary winding SW of the transformer Tr, the sixth switch M6 and the seventh switch M7. Energy is transmitted to the first port P1 through the body diode of the switch M2, the first clamping diode D _Clamp1 and the primary winding PW of the transformer Tr.

After the fourth time instance T4, the fifth switch M5 to the eighth switch M8 are turned off again before the fourth time interval, and then the fifth switch M5 and the eighth switch M8 are turned on again. During the fourth time interval, the current flows through the freewheeling current path of the first freewheeling circuit 110 , that is, through the first diode D1 and the ninth switch M9 . This procedure is repeated until the voltage of the first port P1 is within the first threshold voltage.

The DC-DC converter 100 having a three-port topology can operate in forward mode with the direction of current flowing from the first port P1 to the second port P2 and the third port P3.

In addition, the switches (M1, M2, M3, M4) of the first full bridge 150 can be phase-shifted controlled by the control signals of the first switch M1, the second switch M2, the third switch M3 and the fourth switch M4, etc., wherein, The control signals of the first switch M1 and the second switch M2 are opposite to each other, and the control signals of the third switch M3 and the fourth switch M4 are also opposite to each other. The output voltage of the second port P2 can be modulated by changing the phase shift angle between the gate control signals of the first switch M1 and the third switch M3. In forward mode, the switches (M5, M6, M7, M8) of the second full bridge 160 operate in synchronous rectification mode.

The output voltage of the third port P3 can be modulated by changing the duty ratio of the twelfth switch M12, and the control signals of the first switch M1 and the twelfth switch M12 are synchronized so that the two switches are turned on simultaneously. The eleventh switch M11 and the thirteenth switch M13 work in synchronous rectification mode.

The voltage relationship of different ports (P1, P2, P3) can be expressed as:

V1 is the voltage at the _first port P1 according to the following equation:

V2 is the voltage at the _second port P2 according to the following equation:

V1 is the voltage at the _first port P1 according to the following equation:

_V3 is the voltage at the third port P3 according to the following equation:

Among them, V ₁ is the voltage of the first port P1, V ₂ is the voltage of the second port P2, V ₃ is the voltage of the third port P3, N ₁ is the winding number of the primary winding PW, N ₂ is the voltage of the secondary winding SW Number of windings, N3 is the number of windings _of the center-tapped winding CTW, P _eff is the effective phase shift angle, D _M12 is the duty cycle of switch M12, and D is the duty cycle of switches M5 to M8 or switches M11 and M13.

The DC-DC converter 100 with the three-port topology can operate in the second reverse mode BM2 with the current direction from the third port P3 to the first port P1. When the DC-DC converter 100 operates in the second reverse mode BM2 with the current direction from the third port P3 to the first port P1, the DC-DC converter 100 can be used for:

i) controlling the tenth switch M10 to work in its saturation region,

ii) Turn on the twelfth switch M12;

iii) turning on the eleventh switch M11 within the first time period,

iv) turning off the eleventh switch M11 and the thirteenth switch M13 within a second time period after said first time period,

v) turning on the thirteenth switch M13 within a third time period after the second time period,

vi) turning off the eleventh switch M11 and the thirteenth switch M13 within a fourth time period after the third time period;

Steps iii) to vi) are repeated until the voltage at the DC bus 202 is equal to or higher than the second threshold voltage.

Fig. 6 shows a timing diagram of the switches (M11, M12, M13) and the currents of the second inductance L2, the second diode and the center tap winding. During the second reverse mode BW2 mode, the switch M10 is controlled to work in its saturation region, and the switch M12 is always turned on. During the time interval between the first time instance T1 and the second time instance T2, the switch M11 is turned on, during which time the current at the third port P3 is conducted through the second inductance L2 and the switches M11 and M12, and at At the first port P1, current is fed into the input capacitor of P1 through the body diodes of switches M3 and M2. The switch M11 is turned off at the second time instance T2, and during the time interval between the second time instance T2 and the third time instance T3, the current at the third port P3 flows through the second inductor L2, the second diode tube D2 and switch M10. During the time interval between the third time instance T3 and the fourth time instance T4, the switch M13 is turned on, the current path at the third port P3 is turned on through the second inductance L2 and the switches M13 and M12, and the first port P1 The current at is flowing into the capacitor of the first port P1 through the body diodes of the switches M1 and M4. The switch M13 is turned off at the fourth time instance T4, and after the fourth time instance T4, the port-side current is conducted through the second inductance L2, the second diode D2 and the tenth switch M10. These procedures are repeated until the voltage at the DC bus 202 is equal to or higher than the second threshold voltage. The value of the second threshold voltage can be obtained by the following equation:

Second threshold voltage = V ₃ /N ₃ *N ₁

Wherein, _V3 is the battery voltage at the _third port P3, N1 is the winding number _of the primary winding, and N3 is the winding number of the center-tapped winding CTW.

The DC-DC converter 100 with the three-port topology can also work in a third reverse mode BM3 with the current direction from the second port to the first port P1 and the third port P3. FIG. 7 shows a timing diagram of the DC-DC converter 100 operating in the third reverse mode BM3. In FIG. 7 , the gate control signals of the switches M1 to M8 and M12 , and the currents of the first inductor L1 and the second inductor L2 are shown.

In the third reverse mode BM3, the ninth switch M9 and the tenth switch M10 are turned off, which is not shown in FIG. 7 .

During the first time interval between the first time instance T1 and the second time instance T2, the switches (M5, M6, M7, M8) of the second full bridge 160 are turned on and the secondary winding SW of the transformer Tr is short-circuited. The current of the first inductor L1 increases during the first time interval, as shown in FIG. 7 .

At the second time instance, the fifth switch M5 and the eighth switch M8 are turned off. Current starts to flow through the secondary winding SW of the transformer Tr, and energy is transmitted to the first port P1 through the primary winding PW of the transformer Tr and the first switch M1 and the fourth switch M4. The first switch M1 and the fourth switch M4 are turned on between the third time instance T3 and the sixth time instance T6 to have synchronous rectification and reduce losses. At the sixth time instance T6, the current of the first inductor L1 is controlled below zero.

Before the fifth switch M5 and the eighth switch M8 are turned on at the seventh time instance T7, the first switch M1 and the fourth switch M4 are turned off again at the sixth time instance T6. When the first switch M1 and the fourth switch M4 are turned off, at the sixth time instance T6, the current is forced to stop conducting through the primary winding PW and the secondary winding SW of the transformer Tr. Thus, between the sixth time instance T6 and the seventh time instance T7, current begins to flow through the body diodes of the fifth switch M5 and the eighth switch M8. At the seventh time instance T7, both the fifth switch M5 and the eighth switch M8 are thus conducting at zero voltage and without conduction losses.

Since the inductor current is triangular, it is very important that the lower boundary of the current of the second inductor L2 is lower than zero, so as to realize zero voltage when the fifth switch M5 and the eighth switch M8 are turned on. This modulation, which keeps the lower bound of the current below zero, is called triangular current modulation (TCM), and examples can include:

• The gate signals of switches M5 and M8 are the same, and the gate signals of switches M6 and M7 are the same, but phase shifted by 180 degrees relative to the gate signals of switches M5 and M8. The duty cycle of the switches (M5, M6, M7, M8) is greater than 0.5.

• The voltage and current modulation of the third port P3 is done by controlling the duty cycle of the twelfth switch M12.

• The lower boundary of the current is controlled below zero, eg -3A.

· Before turning on the fifth switch M5 and the eighth switch M8, first turn off the first switch M1 and the fourth switch M4, so as to realize zero-voltage conduction of the fifth switch M5 and the eighth switch M8.

In order to be able to control the lower boundary of the second inductor L2 current, an additional control loop based on a low current boundary controller can be added to the control loop. The input of the low current boundary controller may be a measured low current boundary value, and the output of the low current boundary controller may be the switching frequency of the switch of the present converter. The measured low current limit value can be obtained by one or more current sensors.

Therefore, in the example of the present invention, the DC-DC converter 100 may further include: one or more current sensors, which may be used in the control loop to control the first inductance L1 and/or the second inductance L2 low current boundary value. Therefore, the DC-DC converter 100 may further include at least one of the following components: a first current sensor 180 coupled between the second full bridge 160 and the first side S1 _P2 of the second port P2 and configured to provide a second A set of measured current values; a second current sensor 180', coupled between the Y circuit 170 and the first side S1 _P3 of the third port P3, and used to provide a second set of measured current values; the controller 130, configured to At least one of the first set of measured current values and the second set of measured current values controls the switch of the DC-DC converter 100 .

FIG. 8 shows a three-port DC-DC converter 100 provided by an example of the present invention with a first current sensor 180 and a second current sensor 180'. The first current sensor 180 is coupled between the second full bridge 160 and the first side S1 _P2 of the second port P2, for example, coupled between the fourth connection point 168 of the second full bridge 160 and the first side of the second port P2 Between the underside of S1 _P2 . The second current sensor 180' is coupled between the Y circuit 170 and the first side S1 _P3 of the third port P3, for example, between the third connection point 176 of the Y circuit 170 and the first side S1 _P3 of the third port P3. between the underside.

The first current sensor 180 and the second current sensor 180' provide the low current boundary controller 132 with a first set of measured current values and a second set of measured current values, respectively. The controller 132 is configured to determine the switching frequency of the switches of the DC-DC converter 100 according to the first set of measured current values and the second set of measured current values received from the current sensors 180 and 180 ′. The switching frequency is provided to a controller 130 which controls the switches of the DC-DC converter 100 by providing gate control signals to the transistor gates of the switches. In this way, the controller 130 can control the switches of the DC-DC converter 100 according to the first set of measured current values and the second set of measured current values.

It should be appreciated that the previously discussed two-port and three-port topologies of the DC-DC converter 100 may vary within the scope of the present invention. Therefore, in the following disclosure, non-limiting examples of exemplary three-port topologies are given.

In FIG. 9 , the positions of the first inductor L1 and the first freewheeling circuit 110 (the first diode D1 and the ninth switch M9 ) are changed compared to the topology shown before. In the example shown in FIG. 9 , the first inductor L1 and the first freewheeling circuit 110 are connected to the low voltage side of the second port P2. However, in terms of its functionality, this modification is considered an equivalent circuit to the circuit shown in Figure 3.

In Fig. 10, the positions of the second inductance L2 and the second freewheeling circuit 110' (the second diode D2 and the tenth switch M10) are changed compared to the topology shown before. In the example shown in Fig. 10, the second inductor L2 and the second freewheeling circuit 110' are connected to the low voltage side of the third port P3. However, this modification is also considered to be an equivalent circuit of the circuit shown in FIG. 3 in terms of its function.

In FIG. 11 , the positions of the first inductance L1 , the second inductance L2 , the first freewheeling circuit 110 and the second freewheeling circuit 110 ′ are changed compared to the topology shown before. In the example shown in FIG. 11, the components and circuits are coupled to the low voltage sides of the second port P2 and the third port P3, respectively. However, this modification is also considered to be an equivalent circuit of the circuit shown in FIG. 3 in terms of its function.

Finally, it should be noted that the three-port topologies shown in FIGS. 8 to 10 may include one or more of the above-mentioned first protection circuit 120 , second protection circuit 120 ′, clamping circuit 140 and freewheeling diode D3 .

For example, the processors of the controller 130 and the low current boundary controller 132 may include a central processing unit (Central Processing Unit, CPU), a processing unit, a processing circuit, a processor, an application specific integrated circuit (Application Specific Integrated Circuit, ASIC), a microprocessor or one or more instances of other processing logic that can interpret and execute instructions. Thus, the term "processor" may mean a processing circuit comprising a plurality of processing circuits, such as any, some, or all of the above-listed items. The processing circuitry may also perform data processing functions for inputting, outputting, and processing data, including data buffering and device control functions, such as call processing control, user interface control, and the like.

Finally, it should be understood that the invention is not limited to the examples described above, but also relates to and incorporates all examples within the scope of the appended independent claims.

Claims (14)

1. A DC-DC converter (100), comprising:

a first port (P1) comprising: first side (S1) _P1 ) For coupling to a DC bus (202); second side (S2) _P1 ) Coupled to a first full bridge (M1, M2, M3, M4), wherein the first full bridge (M1, M2, M3, M4) comprises a first switch (M1), a second switch (M2), a third switch (M3) and a fourth switch (M3)A switch (M4);

a transformer (Tr) comprising: a Primary Winding (PW) coupled to the first full bridge (M1, M2, M3, M4); a Secondary Winding (SW) coupled to a second full bridge (M5, M6, M7, M8), wherein the second full bridge (M5, M6, M7, M8) comprises a fifth switch (M5), a sixth switch (M6), a seventh switch (M7) and an eighth switch (M8);

a second port (P2) comprising: first side (S1) _P2 ) Coupled to said second full bridge (M5, M6, M7, M8); second side (S2) _P2 ) For coupling to a first battery (204);

a first inductance (L1) coupled between the second full bridge (M5, M6, M7, M8) and the first side (S1) of the second port (P2) _P2 ) In the middle of;

a first freewheel circuit (110) comprising a first diode (D1) coupled in series with a ninth switch (M9), wherein the first freewheel circuit (110) is coupled in parallel with the first inductor (L1) at the second full bridge (M5, M6, M7, M8) and the first side (S1) of the second port (P2) _P2 ) In the meantime.

2. The DC-DC converter (100) of claim 1, configured to, when operating in a first reverse mode (BM 1) with a current direction from the second port (P2) to the first port (P1):

i) Operating the ninth switch (M9) in a saturation region of the ninth switch (M9);

ii) turn on the fifth switch (M5) and the eighth switch (M8) for a first period of time,

iii) Turning off the fifth switch (M5), the sixth switch (M6), the seventh switch (M7), and the eighth switch (M8) for a second time period after the first time period,

iv) turning on the sixth switch (M6) and the seventh switch (M7) for a third period of time after the second period of time,

v) turning off the fifth switch (M5), the sixth switch (M6), the seventh switch (M7) and the eighth switch (M8) for a fourth period of time after the third period of time;

repeating ii) to v) until the voltage at the DC bus (202) is equal to or above a first threshold voltage.

3. The DC-DC converter (100) of claim 1 or 2, further comprising:

a first protection circuit (120) coupled at the first side (S1) of the second full-bridge (M5, M6, M7, M8) and the second port (P2) _P2 ) And in parallel with said second full bridge (M5, M6, M7, M8).

4. The DC-DC converter (100) of claim 3, wherein the first protection circuit (120) comprises:

a first zener diode (Z1) and a second zener diode (Z2), the first zener diode (Z1) and the second zener diode (Z2) being connected in series with each other and being coupled in opposite directions; or

A first voltage dependent resistor.

5. The DC-DC converter (100) of any of the preceding claims, further comprising:

a third port (P3) comprising: first side (S1) _P3 ) Coupled to the Y circuit (M11, M12, M13); second side (S2) _P3 ) For coupling to a second battery (206), wherein the Y-circuit (M11, M12, M13) is coupled to a center-tapped winding (CTW) of the transformer (Tr) and comprises an eleventh switch (M11), a twelfth switch (M12) and a thirteenth switch (M13).

6. The DC-DC converter (100) of claim 5, wherein a source pin or an emitter pin of each switch is coupled to a common node (N) of the Y-circuit (M11, M12, M13).

7. The DC-DC converter (100) of claim 5 or 6, wherein the first battery (204) is a high voltage battery and the second battery (206) is a low voltage battery.

8. The DC-DC converter (100) of any of claims 5 to 7, further comprising:

a second inductance (L2) coupled at the Y-circuit (M11, M12, M13) and the first side (S1) of the third port (P3) _P3 ) To (c) to (d);

a second free-wheeling circuit (110 ') comprising a second diode (D2) coupled in series with a tenth switch (M10), wherein the second free-wheeling circuit (110') is coupled in parallel with the second inductance (L2) at the Y-circuit (M11, M12, M13) and the first side (S1) of the third port (P3) _P3 ) In between.

9. The DC-DC converter (100) of claim 8, configured to, when operating in a second reverse mode (BM 2) with a current direction from the third port (P3) to the first port (P1):

i) -controlling said tenth switch (M10) to operate in its saturation region,

ii) turning on the twelfth switch (M12);

iii) Turning on the eleventh switch (M11) for a first period of time,

iv) turning off the eleventh switch (M11) and the thirteenth switch (M13) for a second period of time after the first period of time,

v) turning on the thirteenth switch (M13) for a third period of time after the second period of time,

vi) turning off the eleventh switch (M11) and the thirteenth switch (M13) for a fourth period of time after the third period of time;

repeating iii) to vi) until the voltage at the DC bus (202) is equal to or above a second threshold voltage.

10. The DC-DC converter (100) of any of claims 5 to 9, further comprising:

a second protection circuit (120') coupled at the Y-circuit (M11, M12, M13) and the first side (S1) of the third port (P3) _P3 ) In the meantime.

11. The DC-DC converter (100) of claim 10, wherein the second protection circuit (120') comprises:

a third zener diode (Z3) and a fourth zener diode (Z4), the third zener diode (Z3) and the fourth zener diode (Z4) being connected in series with each other and being coupled in opposite directions; or

A second voltage dependent resistor.

12. The DC-DC converter (100) of claim 10 or 11, further comprising:

a freewheeling diode (D3) coupled in parallel with the second protection circuit (120') and forming a freewheeling path when the third port (P3) operates as an output port.

13. The DC-DC converter (100) of any of the preceding claims, further comprising at least one of the following components:

a first current sensor (120) coupled at the second full-bridge (M5, M6, M7, M8) and the first side (S1) of the second port (P2) _P2 ) And for providing a first set of measured current values;

a second current sensor (120') coupled at the Y-circuit (M11, M12, M13) and the first side (S1) of the third port (P3) _P3 ) And for providing a second set of measured current values;

a controller (130) for controlling the switching of the DC-DC converter (100) in dependence on at least one of the first set of measured current values and the second set of measured current values.

14. The DC-DC converter (100) of any of the preceding claims, further comprising:

a clamping circuit (140) comprising a first clamping diode (D) _Clamp1 ) A second clamping diode (D) _Clamp2 ) And a clamping inductance (L) _Clamp ) Wherein, the firstA clamping diode (D) _Clamp1 ) The second clamping diode (D) _Clamp2 ) And said clamping inductance (L) _Clamp ) Is coupled between the first full bridge (M1, M2, M3, M4) and the Primary Winding (PW) of the transformer (Tr).

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